1. Field of the Invention
The present invention relates to a detection apparatus installed in an ink jet printer for detecting residual ink quantity in an ink cartridge supplying ink to an ink jet head, and in particular, relates to a detection apparatus capable of inputting the detected residual ink data directly to a control device of the ink jet printer, thereby the control device can digitally process the residual ink data and the detection apparatus can be simply constructed with low cost, without an A/D converting device such as an A/D converter to conduct A/D conversion of the residual ink data.
2. Description of Related Art
Conventionally, in a printing apparatus such as an ink jet printer, an ink jet head conducts image printing on a print sheet by ejecting ink supplied from an ink cartridge filled with ink. If ink in the ink cartridge is consumed, image printing cannot continue, thus it is necessary to exchange the old ink cartridge with a new one filled with ink before ink is completely consumed, and to supply ink to the ink jet head. Therefore, it is inevitable to install in the ink jet printer an apparatus for continuously detecting residual ink quantity in the ink cartridge.
Under the above circumstance, as the detection apparatuses for detecting the residual ink quantity in the ink cartridge, there are proposed various apparatuses and methods to detect the residual ink quantity.
For example, there exists a detection apparatus that includes a pair of electrode plates that are arranged in the ink cartridge and a condenser is formed between the electrode plates in cooperation with ink, further the residual ink quantity is detected by measuring capacitance which changes according to change of the residual ink quantity. Such detection apparatus will be described with reference to FIG. 18. FIG. 18 shows a circuit diagram of the detection apparatus for detecting the residual ink quantity in the related prior art.
In FIG. 18, a detection apparatus 100 is shown for detecting the residual ink quantity in an ink cartridge 102. The detection apparatus 100 is basically constructed from a signal producing device 101, a pair of electrode plates 103 arranged in the ink cartridge 102, a detecting resistor 104 and an A/D converter 105. The signal producing device 101 produces a rectangular pulse shown in FIG. 19(A). Both the electrode plates 103 construct a condenser C in cooperation with ink filled in the ink cartridge 102. At that time, capacitance of the condenser C changes according to change of the residual ink in the ink cartridge 102. For instance, if enough ink is filled in the ink cartridge 102, the condenser C retains a predetermined capacitance value. On the other hand, if the residual ink quantity decreases by being consumed, the capacitance value of the condenser C becomes small. The detecting resistor 104 outputs to the A/D converter 105 a detecting pulse having a waveform which is rounded in comparison with the rectangular pulse and determined on the basis of the capacitance value of the condenser C and resistance value of the detecting resistor 103, as shown in FIG. 19(B). The A/D converter 105 conducts A/D conversion based on a predetermined voltage value about the detecting pulse, thereafter outputs the A/D conversion value to a control apparatus (not shown).
In the detection apparatus 100, the residual ink quantity in the ink cartridge 102 is detected as follows. That is, the capacitance value of the condenser C constructed from both the electrode plates 103 and ink therebetween becomes small as residual ink decreases, and corresponding to the above, the waveform of the detecting pulse output to the A/D converter 105 in cooperation with the detecting resistor 104 will gradually change. Thus, the residual ink quantity is detected by detecting the changing state of the waveform in the detecting pulse.
In detail, when the rectangular pulse (shown in FIG. 19(A)) is output from the signal producing device 101, the detecting pulse having a rounded waveform (shown in FIG. 19(B)) is output to the A/D converter 105 while enough ink exists in the ink cartridge 102 and the condenser C retains the predetermined capacitance value. On the contrary, when the capacitance value of the condenser C reduces according to decrease of residual ink, the round of the waveform (shown in FIG. 19(B)) in the detecting pulse gradually disappears and the waveform gradually approaches to a waveform of the rectangular pulse. Thus, the detecting pulse with the above waveform is output to the A/D converter 105 and the voltage value converted by the A/D converter 105 becomes higher than the predetermined voltage value, thereby the control apparatus can detect that residual ink is run out of the ink cartridge 102.
However, in the conventional detection apparatus 100, it is necessary to provide the A/D converter 105 which outputs digital data to the control apparatus after A/D conversion of the detecting pulse, and in addition to this, it is necessary to use an interface with complex construction. Therefore, cost of the detection apparatus cannot be reduced and control for detecting the residual ink quantity becomes complex.
Further, as the other detection apparatuses for detecting the residual ink quantity, there are utilized, for example, methods to detect an ink liquid surface by detecting a float having a magnet therein which is movable according to change of the ink liquid surface through a lead switch, or to detect the ink liquid surface through a light sensor. But, in such detection apparatuses, it is necessary to assemble complex parts, thus apparatuses are liable to go wrong. Further, light from the light sensor cannot correctly transmit due to ink attached to the walls of the ink cartridge, as a result, the residual ink quantity cannot be correctly detected.
Under the above circumstance, in order to dissolve the above problems, it is conventionally proposed another type of detection apparatus for detecting the residual ink quantity. In this type of detection apparatus, it is utilized a detection circuit is utilized in which two electrode plates are arranged in the ink cartridge with difference of elevation. The detection circuit detects a resistance value between the electrode plates and guesses the residual ink quantity on the basis of the resistance value. Here, it is known that ink is generally not both a good conductor and an insulating material against electricity, and becomes a conductor with a predetermined resistance value. Therefore, the resistance value between the electrode plates changes according to ink quantity existing therebetween, thus the residual ink quantity can be detected by applying a signal to the detection circuit and measuring the change of resistance value between the electrode plates.
However, in the detection apparatus having the electrode plates in the ink cartridge, though residual ink quantity can be detected with high reliability, there is a problem that a control part for judging change of resistance value inevitably becomes complex. The reason is as follows. That is, the detected signal output from the detection circuit is an analog signal which corresponds to the voltage value change on the basis of the resistance value change between the electrode plates. Therefore, control apparatuses in printers cannot directly process such an analog signal. Thus, it is necessary in the control circuit to provide a converting device such as an A/D converter for converting the analog signal into a digital signal. In addition to this, it is necessary to use an interface with complex construction. Therefore, the detection apparatus inevitably becomes complex and large-scale, and the cost thereof cannot be reduced.